Police have charged a former Arizona State University professor with terroristic threats for allegedly claiming to have explosives Saturday morning as he entered the Liberty Bell Center.

Police identified the man as Carlos J. Balsas, 41, of Tempe, Ariz.

Balsas entered the tourist site shortly after 10 a.m. Saturday, where visitors must pass through a security check. Police said a security officer began to search Balsas's backpack when he stated, "I have explosives in there." He then left.

Security officers notified the U.S. Park Rangers, providing a physical description of Balsas and information on where he was last seen.

When Balsas was stopped by park rangers on the 700 block of Market Street, he was uncooperative, police said. After a brief struggle, he was handcuffed, police said.

Market Street between 7th and 8th Streets was then closed to vehicle and foot traffic around 10:45 a.m. Officers from the Philadelphia Police Department and agents with the Bureau of Alcohol, Tobacco, Firearms, and Explosives arrived on scene, including members of the police bomb squad unit.

Two black backpacks were found outside the Liberty Wheels wheelchair and scooter rental shop at 714 Market St., police said Saturday. Bomb squad officers examined the bags, going back and forth between the bags and the testing equipment in their van. The results came back negative for explosives.

The street was reopened around 11:45 a.m.

Balsas was a professor at Arizona State University, a police source said Sunday, but is no longer employed by the school. At one point, he was an assistant professor at the university's School of Planning, according to a school website.

Balsas is charged with terroristic threats, bomb threats, possessing an instrument of crime, reckless endangerment, and related offenses. The joint investigation was carried out by the Philadelphia Police and FBI.

The U.S. Attorney's Office is expected to take over the investigation Monday.